Electronic circuit systems are typically made by defining complex integrated circuit structures on semiconductor chips, bonding the chips to circuit package substrates, and in turn bonding the packages to printed circuit boards. For such structural bonding, increasing use is being made of "flip-chip" technology in which an element such as a circuit chip is soldered directly to the surface of a substrate rather than being supported by a wire or post affixed to the substrate. A plurality of solder "bumps" are formed on the semiconductor chip, and the chip is aligned on the substrate with each solder bump placed on a metal bonding pad. The unit is then heated so as to melt (reflow) the solder so that when the solder hardens, the chip is bonded to the substrate bonding pads. The same method is often used for surface mounting circuit packages to a printed circuit board.
When the device package comprises a ceramic substrate upon which a complex circuit has been defined which makes connection with several circuit chips mounted on the substrate, the result is usually referred to as a hybrid integrated circuit (HIC). Increasingly, more complex circuits have been defined in integrated circuit chips, leading to a new technology known as very large scale integration (VLSI). To accommodate such complexity, there has arisen a demand for more complex circuitry on the substrate than can be conveniently made on a ceramic substrate. To meet these demands, workers have developed silicon substrates upon which denser circuit patterns can be formed and within which two or more levels of conductors can be formed. Circuit packages of this type are still generally in the developmental stage and are known as advanced VLSI packaging (AVP).
Each AVP package comprises many chips connected to a substrate to form a complex system or subsystem. As a consequence, after the circuit package has been assembled, it is frequently found that one of the chips must be removed for repair or replacement. This can be done by either shearing or melting the solder bonds, removing the chip, and then rebonding a replaced or repaired chip using surface mount techniques as described previously. Such removal also requires removal of the solder remnants left on the bonding pads after removal of the chip. In conventional HIC technology or printed wiring board technology, this can be done by melting the remnants and removing them with vacuum suction. However, when the substrate bonding pads become extremely small, as is characteristic of AVP, it has been found that conventional vacuum suction solder removal often results in splashing of the molten solder onto the substrate and other inconsistencies in the solder removal. We have also tried various techniques for sponging the molten solder from the bonding pads such as using very fine gold-plated copper mesh as a wicking element and using copper powder cakes as a wicking element to soak up the molten solder by capillary action. These devices and techniques have been unsatisfactory because they provide a non-uniform and generally unreliable wicking action across the surface of the substrate.